Method and a device for separation of a surface layer of a liquid body

ABSTRACT

To clean a relatively heavy liquid from small amounts of relatively light liquid the liquids are first introduced into a container, in which the light liquid is allowed to collect on the surface of the heavy liquid. A surface layer of the liquid body in the container, constituting a mixture of the two liquids, is caused to flow over an overflow outlet member into a collecting chamber. From the collecting chamber the liquid mixture is pumped further into a centrifugal separator, wherein the relatively light liquid is separated from the relatively heavy liquid. According to the invention the liquid mixture is pumped from the collecting chamber to the centrifugal separator through a pumping member, which is connected with a rotor of the centrifugal separator and, thus, rotates therewith.

This application is entitled to the benefit of and incorporates byreference essential subject matter disclosed in PCT/SE00/00551 patentapplication filed on Mar. 21, 2000 and Swedish Patent Application9901235-3 filed on Apr. 7, 1999.

FIELD OF THE INVENTION

The present invention relates to a method and a device for removing froma liquid body a liquid mixture, which forms a surface layer on theliquid body, and separating this liquid mixture into one relativelylight liquid and one relatively heavy liquid.

BACKGROUND OF THE INVENTION

In workshops with machine tools for turning and cutting of metal piecesthere is a need for a method and a device of the aforementioned kind forcleaning of liquids used for cooling purposes in the machine tools.Coolants of this kind normally are water based and deteriorate duringuse by, among other things, small amounts of oil being mixed with thecoolant, such as hydraulic oil and lubricating oil, used for theoperation of the machine tools. Oil of this kind causes an unpleasantsmell and makes the coolant unusable in the course of time, if it is notseparated from the coolant. It is known to clean coolants from oil bymeans of a centrifugal separator. In practice, this is performed suchthat a liquid mixture in the form of coolant and undesired oil isallowed to flow from a surface layer of a liquid body, containing thecoolant to be cleaned, over an overflow outlet member into a collectingchamber. The liquid mixture is then pumped from the collecting chamberby means of a pumping device to the centrifugal separator.

Even in other connections there is a need for a method and a device forremoving from a relatively heavy liquid, small amounts of a relativelylight liquid. For example, liquids used for cleaning purposes often musthave light floating contaminants removed therefrom, so that the liquidcan be used anew.

The object of the present invention is to make possible cleaning of arelatively heavy liquid from small amounts of a relatively light liquidin a simple and non-expensive way by means of a simple and inexpensivedevice. The device should be compact and easily mountable to a containerwhich contains liquid to be cleaned. Furthermore, the device should beoperable automatically, and a desired cleaning effect should beobtainable without the need for complicated coordination of theoperation of a centrifugal separator and a pumping device required forpumping the liquid to the centrifugal separator.

SUMMARY OF THE INVENTION

For achievement of this purpose the invention suggests a method ofremoving from a liquid body a liquid mixture, which forms a surfacelayer on the liquid body, and separating this liquid mixture into onerelatively light liquid and one relatively heavy liquid, the liquidmixture being first caused to flow, as previously known, from the liquidbody over an overflow outlet member into a collecting chamber and thenpumped therefrom into a centrifugal separator. The method according tothe invention is characterized in that the liquid mixture is pumped fromthe collecting chamber upwardly and into a rotating centrifugal rotor,forming part of the centrifugal separator, by means of a pumping memberthat is connected with the centrifugal rotor and is rotating therewithand extends down into the liquid mixture in the collecting chamber.Preferably, the overflow outlet member is vertically movable relative tothe pumping member, further liquid mixture being caused to flow overfrom the liquid body to the collecting container in an amount per unitof time corresponding to the capacity of the pumping member and/or thecorresponding centrifugal rotor.

For achieving a desired function of the vertically movable overflowoutlet member a previously known technique may be used. Thus, theoverflow outlet member may be kept floating on said liquid body, inaccordance with U.S. Pat. No. 3,633,749, or be kept floating on theliquid mixture present in said collecting chamber, as set forth in U.S.Pat. No. 5,693,218. Alternatively, a different technology may beemployed for automatic control of the amount of liquid mixture that isto flow over from the surface layer of the liquid body to the collectingchamber. A basic mission for the overflow outlet member is to adapt theflow of new liquid mixture into the collecting chamber to the flow ofliquid mixture pumped up from the collecting chamber to the centrifugalrotor by means of the pumping device.

If the level of the surface layer of the liquid body is changed, it isdesirable that the overflow outlet member automatically adapts itselfthereto. This requires, if the collecting chamber is delimited by acollecting container having certain vertically immobile parts, that atleast part of one wall of the collecting container is vertically movabletogether with the overflow outlet member.

In a preferred embodiment of the invention a collecting container wallpart of this kind includes a bellows but, alternatively, sealing devicesof different kinds may be used between the overflow outlet member andvertically immobile parts of the collecting container.

For cleaning of a liquid mixture, which has been transferred in theabove described manner from the surface layer of a liquid body to acollection container for further transportation to a centrifugalseparator, it is suggested according to the invention that thecentrifugal separator includes a centrifugal rotor, which is connectedwith a pumping device adapted to extend from above and downwards intothe liquid mixture present in the collecting container. The centrifugalseparator further includes a driving device, which is adapted to drivethe centrifugal rotor as well as the pumping device connected therewithwherein the pumping device is adapted to pump the liquid mixture to andinto the centrifugal rotor. The pumping device may be designed in manydifferent ways. Preferably, it includes a pumping member which isdirectly connected with the centrifugal rotor so that the common drivingdevice may be adapted for rotation of both, the centrifugal rotor andthe pumping member through one and the same transmission device.However, this is not absolutely necessary according to the invention.Alternatively, the driving device may be coupled separately to thepumping member, in which case a gear device of one kind or another maybe used between the driving device and one of the centrifugal rotor andthe pumping member. Most important is that an increased rotational speedof the pumping member, meaning an increased liquid flow to thecentrifugal rotor, brings with it a corresponding increase of theseparation capability of the centrifugal rotor as a consequence of anincreased rotational speed thereof.

In a preferred embodiment of the invention a pumping device includes atubular pumping member, which is rotatable around a substantiallyvertical rotational axis, the pumping member defining a central pumpingchannel for conducting liquid mixture from the collection container tothe centrifugal rotor. Preferably, both the centrifugal rotor and thepumping member are rotatable around said vertical rotational axis, andin the preferred embodiment the pumping member, as mentioned, isdirectly connected with the centrifugal rotor for rotation togethertherewith. A pumping device of this kind does not subject the liquid tolarge shear forces. Shear forces of this kind are disadvantageous inthis connection, since they cause undesired formation of emulsion of thetwo liquids to be separated from each other in the centrifugalseparator.

The method and the device according to the invention may be used forcontinuous cleaning of a liquid, cleaned liquid being returned directlyto said liquid body. The cleaned liquid is preferably returned to alevel below the predetermined surface layer of the liquid body, so thatthe pre-separation having occurred in the liquid body is disturbed aslittle as possible. In the device according to the invention thereturning is made by means of a stationary casing, which surrounds thecentrifugal rotor and which has a returning member extending down intothe liquid body to said level.

As mentioned, the rotatable pumping member extending down into theliquid to be cleaned is preferably tubular. For minimizing the wettedsurface of the pumping member and/or for avoiding that liquid is pumpedupwardly on the outside of the pumping member, the present inventionprovides a non-rotatable wall adapted to extend from above and down intothe liquid mixture. During operation of the device, a sealing deviceprovided in the collecting container is arranged to seal between thenon-rotatable wall and the rotatable pumping member. The sealing devicemay have any suitable design. For instance, an annular lip gasket ofrubber or some other elastic material may be supported by thenon-rotatable wall and surround the pumping member and seal radiallyagainst the outside thereof. Alternatively, a similar annular lip gasketmay be supported by the rotatable pumping member, so that by means ofthe centrifugal force it may be kept pressed radially outwardly againstthe surrounding non-rotatable wall.

In a preferred embodiment of the invention the sealing device includesan annular axially movable sealing member and means adapted toaccomplish an axial sealing force between the non-rotatable wall ornon-rotatable members connected therewith and the rotatable pumpingmember. The sealing member may be rotatable together with the pumpingmember, but preferably it is non-rotatable and adapted to be pressedaxially against a sealing surface, preferably an end surface of therotatable pumping member.

A non-rotatable wall of the aforementioned kind, which surrounds thepumping member, protects against unintentional contacts with the pumpingmember during rotation thereof.

If the centrifugal rotor is suspended from a flexible suspension device,said non-rotatable wall is preferably suspended from the same flexiblesuspension device for avoidance of relative pendulum movements betweenthe rotatable and non-rotatable sealing surfaces of the sealing deviceduring operation of the centrifugal rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described following with reference to the accompanyingdrawings, in which:

FIG. 1 is a side elevational view of a separation device according tothe present invention shown mounted on a container containing liquid tobe treated in the separation device. The container is shown in a sectionview.

FIG. 2 is a partly in section view of the separation device andcontainer of FIG. 1.

FIG. 3 is a partial enlarged view of the separation device of FIG. 2.

FIG. 4 is a sectional view of the separation device of FIG. 3 takenalong the line 4—4 in FIG. 3.

FIG. 5 is a sectional view of the separation device of FIG. 3 takenalong the line 5—5 in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show a container 1 containing liquid, which may beintended for use as a coolant in machine tools for turning or cutting ofmetal pieces. Liquid of this kind may be water based, and deterioratesupon use due to the presence of small amounts of oil. Used coolantenters the container 1 through an inlet 2 and cleaned coolant leaves thecontainer through an outlet 3 to be reused. While the coolant is presentin the container 1 it forms a liquid body 4, in which the oil iscollected in a thin surface layer at the top of the liquid body 4.

The container 1 has a horizontal upper limiting wall 5 having an opening6, through which a separation device according to the invention extendsfrom above and down into the container. The separation device, whichforms a self sustaining unit mounted onto the container 1, includes acasing 7, which is suspended from the upper limiting wall 5 of thecontainer through a flexible suspension device 8. Only one of threealike parts of the suspension device 8 is shown in the drawing.Furthermore, the separation device includes a motor 9, which is fastenedto the upper part of the casing 7, and a centrifugal rotor 10 (FIG. 2)suspended from the motor and surrounded by the casing 7. The motor isadapted to drive the centrifugal rotor 10 around a vertical rotationalaxis R.

The separation device further includes a collecting container 11, whichis supported by the casing 7 within the container 1 in a way such thatit is surrounded by the liquid body 4. The collecting container 11includes a bottom plate 12, a surrounding wall in the form of a bellows13 circular in cross section and fastened at its lower part to thebottom plate 12, and an annular floater 14, which is fastened to theupper part of the bellows 13. The floater 14 is adapted to float on theliquid body 4 and to form an overflow outlet member, over which asurface layer of the liquid body 4 may flow into the collectingcontainer 11. The upper side of the floater has several radial recessesor grooves, through which the liquid may flow into the collectingcontainer evenly distributed around the whole of the floater. Thegrooves give to the floater a stability, so that it moves the sameextent vertically around the whole of its circumference.

FIG. 2 shows that the collecting container 11 delimits a collectingchamber 15 for a liquid mixture entering therein through the overflowoutlet member (the floater) 14. The liquid mixture consists mainly ofcoolant, which is relatively heavy, and a small amount of oil, which isrelatively light. Furthermore, FIG. 2 shows that the bottom plate 12 ofthe collecting container is supported by a casing 7 by means of a sleeve16.

At its lower part the centrifugal rotor 10 carries a tubular, slightlyconical pumping member 17, which extends down into the collectingchamber 15. The pumping member 17, which is fastened to the centrifugalrotor 10 by means of a lock ring 18, is surrounded by a substantiallycylindrical non-rotatable wall 19, which is supported by the casing 7and extends from an area above the liquid body 4 down into thecollecting chamber 15. At its lower part the wall 19 carries a sealingdevice 20 adapted to seal against the lowermost part of the pumpingmember 17, so that liquid mixture present the collecting chamber 15 willnot get into contact with the outside of the pumping member 17. Thesealing device 20 is described in detail below with reference to FIG. 3.

The centrifugal rotor 10 may be of a conventional kind and is thereforenot described in detail. For a closer description of the centrifugalrotor of a suitable kind reference is made to, for instance, EP 312 233B1, EP 312 279 B1, WO 96/33021 and WO 96/33022.

The centrifugal rotor 10 has an inlet chamber 21, which through achannel 22 communicates with a separation chamber 23. Furthermore, thecentrifugal rotor 10 has a first outlet 24 for a separated relativelylight liquid, in this case oil, and a second outlet 25 for a separatedrelatively heavy liquid, in this case water based coolant. The casing 7has a first outlet 26 adapted to receive separated oil leaving thecentrifugal rotor through its outlet 24 and a second outlet 27 adaptedto receive separated coolant leaving the centrifugal rotor through itsoutlet 25.

Separated oil is conducted through the outlet 26 to some suitablerecipient therefor, whereas separated coolant is conducted throughspaces in the casing 7 back to the liquid body 4. Thus, the casing 7 isformed so that separated coolant is conducted on the outside of thestationary wall 19, which surrounds the pumping member 17, down to andthrough the aforementioned sleeve 16. As can be seen in FIG. 2, there isdelimited within the casing 7 a return chamber 28, in which returnedcleaned coolant forms a liquid body, the free liquid surface of whichduring operation of the separation device will be present somewhat abovethe liquid surface of the liquid body 4.

FIG. 3 shows in a larger scale than FIG. 2 the collecting container 11and the sealing device 20. As shown in FIG. 3, the sealing device 20includes an axially movable sealing member 29. The sealing member 29 isadapted by means of a sleeve formed upper portion to seal against theinside of the stationary cylindrical wall 19 and by means of an annularlower portion to seal against the rotatable pumping member 17. A screwspring 30 resting on wings 31 is adapted to press the sealing member 29upwards, with reference to FIG. 3, into sealing engagement with thepumping member 17. For this purpose, the pumping member 17 carries atits lowermost part a sealing member 32 rotatable therewith. The sealingmembers 29 and 32 abut against each other through axially facing sealingsurfaces.

The wings 31 are connected with the bottom plate 12 and are intended,apart from supporting the spring 30, for counteracting rotation ofliquid in the collecting container 15 in the area of the lower part ofthe pumping member 17. As shown in FIG. 3, at least one of the wings 31extends all the way up to the inlet opening of the pumping member 17 inthe area of the sealing member 32.

FIG. 4 shows a section through the pumping member 17 along the line 4—4of FIG. 3 illustrating the pumping member 17 having three internalaxially and radially extending wings 33 intended for entrainment ofliquid in the rotation of the pumping member.

FIG. 5 shows a section through the casing 7 along the line 5—5 of FIG.3. As shown, the outside of the casing 7 has three wings 34 extendingboth radially and axially therefrom. The wings 34 have, like the wings31, a function of counteracting rotation of liquid in the collectingchamber 15.

The separation device according to the invention operates in thefollowing manner:

The floater 14 is formed such that, as long as no liquid is present inthe collecting container 11, it may float on the liquid body 4 but onlyat a level such that a surface layer of the liquid body 4 flows over thefloater 14 and into the collecting container 11. When the liquid surfacein the collecting container 11 approaches the floater 14, the floater isactuated also by the liquid in the collecting container 11. Then, thefloater 14 is lifted up to a level such that it blocks further inflow ofliquid into the collecting container 11. This occurs before the liquidsurface in the collecting container 11 has reached up to the same levelas the liquid surface in the surrounding container 1.

When the motor 9 is started for driving the centrifugal rotor 10 and thepumping member 17 connected therewith around the rotational axis R,liquid is pumped from the collecting container 11 upwardly through thepumping member 17 and into the centrifugal rotor 10. The liquid surfacewill then sink in the collecting container 11, whereby also the floater14 will sink somewhat, and new liquid will flow into the collectingcontainer 11 from the surface layer of the liquid body 4. If an evenflow of liquid is pumped out of the collecting container 11, the liquidsurface therein will be adjusted to a certain level, as can be seen inFIGS. 2 and 3, and the same amount of liquid will flow in via thefloater 14 out through the pumping member 17.

In the pumping member 17 a substantially cylindrical liquid surface willbe formed, as is illustrated in FIG. 2, which extends all the way fromthe lower part of the pumping member to the inlet chamber 21 of thecentrifugal rotor. In the liquid body, which is thus formed in thepumping member 17 and which is entrained in its rotation by the wings 33(see FIG. 4), liquid flows axially upwardly as illustrated by means ofarrows in the FIGS. 2 and 3. Centrally in the pumping member 17 there isleft an air filled space which, if desired, may communicate with airsurrounding the pumping member 17. For this purpose the pumping member17 may carry a small pipe, which extends from the centre of the pumpingmember radially outwardly to the outside of the pumping member. A pipeof this kind is indicated by dotted lines in FIG. 2 at the upper part ofthe pumping member 17.

Liquid entering the inlet chamber 21 of the centrifugal rotor 10 throughthe pumping member 17 is conducted therefrom through the inlet channel22 into the separation chamber 23. In this chamber there is arranged aset of conical separation discs, which between themselves form thinseparation spaces. In the separation spaces the small drops of oilsuspended in the coolant are separated by being forced by thecentrifugal force to move towards the rotational axis of the centrifugalrotor and out through the outlet 24. The coolant freed from oil firstflows in a direction from the rotational axis of the centrifugal rotorout of said separation spaces and then through one or more collectingchannels back towards the rotational axis to the centrifugal rotoroutlet 25 for cleaned coolant.

Whereas separated oil is conducted through the outlet 26 in the casing 7to a particular recipient therefore, the cleaned coolant is conductedthrough the outlet 27 back to the liquid body 4 in the container 1.Thus, the coolant is conducted from the outlet 27 to the return chamber28 and from there through the pipe 16 out into the liquid body 4.

Since the amount of oil separated from the coolant is extremely small,there is returned to the liquid body 4 a flow of liquid which issubstantially of the same magnitude as that passing via the floater 14into the collecting container 11. A certain difference as to levelscomes up between the liquid surfaces in the return chamber 28 and in thesurrounding container 1, respectively, as illustrated in the FIGS. 2 and3.

As also illustrated in the FIGS. 2 and 3, there are formed in the areaof the floater 14 two particular liquid surfaces immediately inside andoutside, respectively, the bellows 13. These liquid surfaces are formedbecause air has been enclosed on the underside of the floater bothinside and outside the collecting container 11. It should be mentioned,that the overpressure coming up in the air thus trapped contributes tothe floating ability of the floater 14.

As can be understood, the floater 14 adapts its position to the amountof liquid present in the container 1, whereas the bottom plate 12 ismaintained at an unchanged level. Furthermore it can be understood, thatthe pumping capacity of the pumping member 17 is automaticallyincreased, if the separation capacity of the centrifugal rotor isincreased by increasing of its rotational speed. Upon such an increaseof the pumping capacity the inflow of liquid into the collectingcontainer 11 from the liquid body 4 automatically increases.

The collecting container 11 need not necessarily be carried by thecasing 7, which surrounds the centrifugal rotor 10 and the pumpingmember 17. Alternatively, it may be supported by the container 1, e.g.stand on its bottom. Also, the stationary wall 19, which surrounds thepumping member 17 and supports part of the sealing device 20, need notbe carried by the casing 7. Even the wall 19 may alternatively becarried by the container 1. However, the arrangement shown in thedrawing is advantageous for several reasons. Thus, for the function ofthe sealing device 20 it is advantageous that both of the co-operatingsealing members 29 and 32 are carried by one and the same suspensiondevice. Since a suspension device for the rotatable centrifugal rotor 10should be flexible and thus, the rotatable part of the sealing device 20becomes flexibly suspended, also the non-rotatable part of the sealingdevice should be flexibly suspended. Furthermore, since thenon-rotatable wall 19 around the pumping member 17 is preferablyflexibly suspended, it is also advantageous that the collectingcontainer 11 is flexibly suspended from the same suspension advice.Thereby, for instance the wall 19 or other members connected therewithmay be used for guiding the vertical movements of the floater 14. In theshown arrangement the wings 34 (see FIG. 5) are used for such guiding.

What is claimed is:
 1. A device for removing from a liquid body a liquidmixture which forms a surface layer on the liquid body, and separatingthe liquid mixture into one relatively light liquid and one relativelyheavy liquid, the device comprising: a vertically movable overflowoutlet member adapted to be overflowed by the liquid mixture from thesurface layer of the liquid body, a collecting container adapted toreceive the liquid mixture having overflowed the overflow outlet member,a centrifugal separator adapted to receive the liquid mixture from thecollecting container and to separate it into the relatively light liquidand the relatively heavy liquid, the centrifugal separator including acentrifugal rotor connected with a pumping device extending down intoliquid mixture in the collecting container, the centrifugal separatorfurther including a driving device, adapted to drive the centrifugalrotor as well as the pumping device connected therewith, and wherein thepumping device is adapted to pump the liquid mixture to and into thecentrifugal rotor.
 2. A device according to claim 1, wherein the pumpingdevice includes a pumping member connected to the centrifugal rotor androtatable therewith around a rotational axis common to the pumpingmember and the centrifugal rotor.
 3. A device according to claim 2,wherein the pumping member is tubular and has a central pumping channelfor pumping the liquid mixture from the collecting container to thecentrifugal rotor.
 4. A device according to claim 2, wherein thecentrifugal rotor and the pumping member are rotatable around asubstantially vertical rotational axis.
 5. A device according to claim2, wherein the pumping member is surrounded by a non-rotatable wallextending down into the liquid mixture in the collecting container and asealing device is adapted to seal between the non-rotatable wall and therotatable pumping member so that the liquid mixture is prevented frommoving upwardly on the outside of the pumping member as a consequence ofthe rotation thereof.
 6. A device according to claim 5, wherein thecentrifugal rotor is suspended from a flexible suspension device and thenon-rotatable wall is also suspended from the flexible suspension devicefor avoiding relative pendular movements between the non-rotatable walland the rotatable pumping member during operation of the centrifugalrotor.
 7. A device according to claim 5, wherein the sealing devicecomprises an annular axially movable sealing member and means adapted toaccomplish an axial sealing force between the non-rotatable wall and therotatable pumping member.
 8. A device according to claim 7, wherein theannular sealing member is non-rotatable and adapted to be pressedaxially against the rotatable pumping member.
 9. A device according toclaim 8, wherein the pumping member is tubular and the non-rotatablesealing member is adapted to be pressed against an end surface definedby the rotatable pumping member.
 10. A device according to claim 5,wherein the collecting container is suspended from the non-rotatablewall.
 11. A device according to claim 10, wherein the centrifugal rotoris surrounded by a casing which delimits spaces for receiving separatedrelatively heavy liquid and conducting the relatively heavy liquid via apassage extending through the collecting container to the liquid body.12. A device according to claim 1, wherein members are arranged in thecollecting container for counteracting liquid rotation therein.
 13. Adevice according to claim 1 wherein means are provided for overflowoutlet member floating on one of said liquid body and said liquidmixture in the collecting container.
 14. A method according to claim 13,in which the separated relatively heavy liquid is conducted back to theliquid body via a passage extending through the collecting chamber. 15.A method of removing from a liquid body a liquid mixture, which forms asurface layer on the liquid body, and separating the liquid mixture intoone relatively light liquid and one relatively heavy liquid, the methodcomprising the steps of: causing the liquid mixture to flow from theliquid body over an overflow outlet member into a collecting chamber;pumping the liquid mixture from the collecting chamber into acentrifugal separator; the pumping being accomplished by rotating apumping member extending down into the liquid mixture in the collectingchamber and transferring the liquid mixture upwardly into a centrifugalrotor rotating with the pumping member, the pumping member beingconnected to the centrifugal rotor; and wherein the overflow outletmember floats on one or both of the liquid body and the liquid mixturepresent in the collecting chamber.
 16. A method of removing from aliquid body a liquid mixture, which forms a surface layer on the liquidbody, and separating the liquid mixture into one relatively light liquidand one relatively heavy liquid, the method comprising the steps of:causing the liquid mixture to flow from the liquid body over an overflowoutlet member into a collecting chamber; pumping the liquid mixture fromthe collecting chamber into a centrifugal separator; the pumping beingaccomplished by rotating a pumping member extending down into the liquidmixture in the collecting chamber and transferring the liquid mixtureupwardly into a centrifugal rotor rotating with the pumping member, thepumping member being connected to the centrifugal rotor; and wherein theoverflow outlet member is vertically movable relative to the pumpingmember, the method further including causing the liquid mixture to flowfrom the liquid body to the collecting chamber at the same rate as thatby which the liquid mixture is pumped by means of the pumping memberinto the centrifugal rotor.
 17. A method of removing from a liquid bodya liquid mixture, which forms a surface layer on the liquid body, andseparating the liquid mixture into one relatively light liquid and onerelatively heavy liquid, the method comprising the steps of: causing theliquid mixture to flow from the liquid body over an overflow outletmember into a collecting chamber, the liquid being conducted into thecollecting chamber around an entire circumference defined by the pumpingmember; pumping the liquid mixture from the collecting chamber into acentrifugal separator; and wherein the pumping is accomplished byrotating a pumping member extending down into the liquid mixture in thecollecting chamber and transferring the liquid mixture upwardly into acentrifugal rotor rotating with the pumping member, the pumping memberbeing connected to the centrifugal rotor.
 18. A method of removing froma liquid body a liquid mixture, which forms a surface layer on theliquid body, and separating the liquid mixture into one relatively lightliquid and one relatively heavy liquid, the method comprising the stepsof: causing the liquid mixture to flow from the liquid body over anoverflow outlet member into a collecting chamber; pumping the liquidmixture from the collecting chamber into a centrifugal separator; thepumping being accomplished by rotating a pumping member extending downinto the liquid mixture in the collecting chamber and transferring theliquid mixture upwardly into a centrifugal rotor rotating with thepumping member, the pumping member being connected to the centrifugalrotor; the liquid mixture the pumped upwardly through the rotatingpumping member from the collecting chamber to the centrifugal rotor; andwhile the liquid mixture is still in the collecting chamber, the liquidmixture is kept separate from contact with the outside of at least partof the pumping member by means of a sealing device.
 19. A method ofremoving from a liquid body a liquid mixture, which forms a surfacelayer on the liquid body, and separating the liquid mixture into onerelatively light liquid and one relatively heavy liquid, the methodcomprising the steps of: causing the liquid mixture to flow from theliquid body over an overflow outlet member into a collecting chamber;pumping the liquid mixture from the collecting chamber into acentrifugal separator; the pumping being accomplished by rotating apumping member extending down into the liquid mixture in the collectingchamber and transferring the liquid mixture upwardly into a centrifugalrotor rotating with the pumping member, the pumping member beingconnected to the centrifugal rotor; and returning the relatively heavyliquid to the liquid body at a level below the surface layer of theliquid body.